In conventional gas turbine engines, as shown in FIG. 1, combustion gases created within a combustor 10 are passed to a turbine assembly via a plurality of transition ducts 12. In many conventional systems, the transition ducts 12 extended longitudinally without any offset in a circumferential direction. A row of first stage vanes 14 were used to turn the combustion exhaust gases before being passed to the row one turbine blades 16. The use of first stage vanes 14 in a turbine assembly to accelerate and turn the longitudinal combustor exhaust gas flow in the circumferential direction presented several challenges. The vanes 14 and the associated vane support structures were required to have high strength characteristics to withstand the forces generated in changing the direction of extremely hot, high pressure gas flow over a substantial angle in a relatively short distance. The temperature of the gas flow and the heat generated by this turning process also require a vane cooling system. The forces and heat involved diminished material properties causing cracks to develop and otherwise damage the vanes and associated support structures.
To accommodate these operating conditions and to provide a more robust design, as shown in FIGS. 2-10, the transition ducts 20 directing combustion gases from a combustor 22 to a turbine assembly 24 were skewed circumferentially such that the outlets 26 of the transition ducts 20 were skewed circumferentially in the same direction that the first row turbine vanes would otherwise skew the combustion exhaust gases. As such, row one turbine vanes were no longer needed because the exhaust gases emitted from the transition ducts 20 already included the correct circumferential vector, thereby eliminating the need for the row one turbine vanes. As shown in U.S. Pat. No. 8,113,003, filing date Aug. 12, 2008, issuance date Feb. 14, 2012, which is incorporated herein in its entirety, the outlet of each transition duct is skewed in the circumferential direction relative to the inlet of each transition duct. While the transition duct system of the U.S. Pat. No. 8,113,003 has eliminated the need for row one turbine vanes upstream of row one turbine blades within a turbine assembly, there exists a need to increase the useful life of the skewed transition duct system by eliminating areas of high stress, which are shown in FIGS. 6-10.